Reduction of vibrations in a drivetrain

Abstract

A powertrain (10) comprises an electric motor (16) and an internal combustion engine (12) coupled together. A method for reducing vibrations in the powertrain (10) comprises: receiving a motor speed signal (30) from the electric motor (16); determining a target speed signal (32) for the internal combustion engine (12) by modifying the motor speed signal (30) into an envelope signal (34); and applying the target speed signal (32) to the internal combustion engine (12). The envelope signal (34) is calculated by detecting local maxima (36) of the motor speed signal (30), and the envelope signal (34) is adjusted to the value of the local maximum (36) until a time period (37) has elapsed since the local maximum.

Description

[0001] The invention relates to a method, a computer program, a computer-readable medium, and a control device for reducing vibrations in a drive train. The invention also relates to the drive train itself.

[0002] In hybrid vehicles, the combustion engine is usually coupled to the electric motor via a clutch. The electric motor, which, like the combustion engine, powers the vehicle, can also be used to start the combustion engine. For this, the clutch is engaged, and the combustion engine is driven and synchronized by the already running electric motor. During the synchronization process, a target speed for the combustion engine is calculated from the speed of the electric motor. However, the engine speed signal may be delayed due to transmission via a data communication bus and the resulting target speed. Therefore, the engine speed must be delayed by taking into account its own gradient, multiplied by a constant factor.If vibrations or noise are present in the motor speed, the delay compensation amplifies the vibrations of the internal combustion engine's target speed, causing the target speed to cross the motor speed multiple times. In such a case of intersecting speeds, a clutch algorithm causes the clutch to engage and disengage repeatedly due to a false detection of speed synchronization. This can lead to vibrations in the drivetrain. In other words, the delay compensation amplifies the vibrations or noise inherent in the electric motor.

[0003] One solution to reduce these vibrations is to limit the downward gradient of the target speed for the combustion engine during synchronization. However, this solution does not allow the downward gradients to be completely eliminated. Thus, while the target speed vibrations have a significantly lower amplitude than the speed signal of the electric motor, they are still present.

[0004] It is an object of the invention to further reduce the vibrations and noise caused by the aforementioned delay compensation calculation in the drive train.

[0005] This objective is achieved by the subject matter of the independent claims. Further exemplary embodiments are described in the dependent claims and the following description.

[0006] One aspect of the invention relates to a method for reducing vibrations in a powertrain. The powertrain comprises an electric motor and an internal combustion engine coupled together. The method can be carried out automatically by a control device or control system of the powertrain. The powertrain can be configured to drive a hybrid vehicle.

[0007] According to one embodiment, the method comprises the following: receiving a motor speed signal from the electric motor; determining a target speed signal for the internal combustion engine by modifying the motor speed signal into an envelope signal; and applying the target speed signal to the internal combustion engine. The motor speed signal can be provided by a control unit of the electric motor. The motor speed signal can be measured, for example, with a speed sensor of the electric motor. The target speed signal can be determined by another control unit, such as a transmission coupled to the electric motor and the internal combustion engine. The target signal can be applied to the internal combustion engine via another control unit, which further controls the speed of the internal combustion engine. These control units may be components of a hardware-implemented control unit and / or control system.In particular, the control devices can be interconnected via a data communication bus, which can delay the engine speed signal and / or the target speed signal.

[0008] The engine speed signal and / or the target speed signal, as well as all signals mentioned here, can be digital signals, i.e., a series of values, where each value is assigned to a point in time.

[0009] According to one embodiment, the envelope signal is calculated by detecting a local maximum of the engine speed signal, setting the envelope signal to the value of the local maximum after the local maximum, and resetting the envelope signal to the engine speed signal when a time period starting with the local maximum has elapsed.

[0010] Local maxima of the speed signal are detected, and the envelope signal is set to the value of a previous local maximum until a time period beginning with the local maximum has elapsed. Alternatively, the envelope signal can be set to the motor speed signal. The time period can be of a fixed length and / or chosen based on an average period of the expected oscillations. For example, the time period can be between 50 µs and 400 µs.

[0011] A local maximum can be detected by comparing values ​​within a time window. If the highest value within a time window is not at the edge of the time window, the highest value can be identified as the local maximum.

[0012] When a local maximum is detected, the subsequent values ​​of the envelope signal are set to the value at the local maximum. This results in an envelope signal with zero gradients. When a time period beginning at the time of the local maximum ends, the envelope signal is reset to the engine speed signal; that is, the value of the envelope signal at a given time is set to the value of the engine speed signal at that time. If a new local maximum is detected, the envelope signal is set to the value of the new local maximum.

[0013] In this way, if oscillations with a shorter period than the time period are present in the engine speed signal during engine start, the envelope signal, and therefore the target speed signal, only increase. This significantly reduces the oscillations in the target speed.

[0014] According to one embodiment, the envelope signal is adjusted to the motor speed signal when the motor speed signal rises above the local maximum. When the value of the local maximum becomes less than the actual value of the motor speed signal, the values ​​of the envelope signal are subsequently adjusted to match the motor speed signal. This continues until the next local maximum is detected. In this way, jumps in the envelope signal can be avoided while the envelope signal still exhibits a non-negative gradient.

[0015] According to one embodiment, a gradient signal is determined from the filtered engine speed signal, and the local maxima can be determined either from zero crossings of the gradient signal or by comparing previous gradient values ​​(e.g., 2 or 3 cycle times old) with the current cycle value of the gradient, i.e., where the gradient changes its direction from an increasing tendency to a decreasing tendency. The gradient signal is an indicator of a gradient in the engine speed signal. The gradient signal can be determined by measuring the differences between successive values ​​of the engine speed signal. When the gradient signal changes from positive to negative values, a local maximum of the engine speed signal can be detected. Since filtering the engine speed typically adds a delay to the signal (typically, for example, 1 / 3 of a cycle), the gradient signal can be used to determine the local maximum of the engine speed signal.40 ms to 50 ms), the alternative of detecting local maxima by gradient changes is preferred over detecting zero crossings, since the local maxima calculated by zero crossings may not correspond to the actual local maxima of the motor speed on a time axis.

[0016] According to one embodiment, the target speed signal is determined by adding an offset signal to the envelope signal. The offset signal is set to an offset value if oscillations are detected in the speed signal; otherwise, the offset signal is set to zero. The offset value can be a calibrated value selected with respect to the expected amplitudes of the engine speed signal. The offset value is calculated or calibrated using a multiplication factor for the envelope signal (e.g., 5% of the signal; 100 rpm becomes 105 rpm). Oscillations can be detected if local maxima, or more generally, local extrema, are spaced less than a oscillation time window apart.

[0017] The offset added to the envelope signal ensures that the target speed signal is higher than the engine speed signal during oscillations, so that even a delayed target speed signal does not lead to a reduction in the combustion engine speed by the corresponding control unit. The target speed signal maintains a distance from the engine speed signal, resulting in smoother synchronization of the combustion engine with the electric motor.

[0018] According to one embodiment, to detect vibrations, a first gradient signal and a second gradient signal are determined from the speed signal, wherein the second gradient signal is smoothed with respect to a wider moving time window than the first gradient signal. The gradient signal determined from the motor speed signal can be smoothed with two different moving time windows. For example, averaging can be performed with a corresponding moving time window. The first time window can be significantly shorter than the second time window. It is also possible that the first gradient signal is the gradient signal. The second moving time window for smoothing can be at least five times wider than the first moving time window.

[0019] The first gradient signal can be compared to a band around the second gradient signal, where the band can be defined by adding and subtracting a threshold value from the second gradient signal. If the first gradient signal leaves and re-enters the band within one oscillation time period, oscillations can be detected. This band threshold can depend on the actual gear ratio or the motor speed; that is, the higher the motor speed, the higher the band threshold.

[0020] According to one embodiment, oscillations are detected when, firstly, the first gradient signal drifts out of a band around the second gradient signal, and secondly, the first gradient signal crosses the second gradient signal within an oscillation time window that begins with the first crossing. In this way, a peak of an oscillation can be detected and / or oscillations can be detected rapidly. The oscillation time window can be chosen with respect to an expected oscillation length. The first gradient signal can drift out of a band around the second gradient signal if the absolute value of the difference between the first gradient signal and the second gradient signal exceeds a threshold. The threshold can be determined with respect to an expected amplitude of the gradient signal.

[0021] According to one embodiment, oscillations are detected if, in addition: thirdly, the first gradient signal drifts out of the band around the second gradient signal on the other side of the band within the oscillation time period, and the first gradient signal crosses the second gradient signal minus the threshold value within the oscillation time period; and then, fourthly, the first gradient signal crosses the second gradient signal again within the oscillation time period. Drifting out of the band on the other side means that the difference between the first gradient signal and the second gradient signal has the opposite sign compared to the previous case.

[0022] Whenever a band outage or crossing is detected, a timer is started that ends after the oscillation period. If the timer ends before a band outage or crossing is detected, the oscillation detection is reset.

[0023] According to one embodiment, the velocity signal is filtered before the envelope signal is calculated to remove ripples, i.e., to attenuate higher frequencies. The filtering can be performed using a low-pass filter. For example, averaging can be carried out using a sliding window.

[0024] According to one embodiment, the combustion engine and the electric motor are coupled by a clutch. This coupling clutch can be partially closed and / or opened to couple the combustion engine to the electric motor.

[0025] According to one embodiment, the method is performed during the synchronization of the internal combustion engine with the electric motor, provided the clutch is partially disengaged during this process. Outside of synchronization, the method can be stopped, and the same target speed signal can be applied to both the electric motor and the internal combustion engine.

[0026] According to one embodiment, the method is performed during the start-up of the internal combustion engine, e.g., during the engagement of the clutch. The method can be performed when the speed of the internal combustion engine is ramped up to the speed of the electric motor. That is, initially the speed of the internal combustion engine is zero and the clutch is fully open, and at the end the speed of the internal combustion engine is equal to the speed of the electric motor and the clutch is fully engaged.

[0027] Another aspect of the invention relates to a computer program with instructions which, when executed by a processor, cause the processor to perform the method described herein. Such a processor can be part of a computer and / or a control unit of the powertrain. It is also conceivable that the method is carried out by at least two processors, which can be part of at least two control units.

[0028] Another aspect of the invention relates to a computer-readable medium in which such a computer program is stored. A computer-readable medium can be a non-volatile medium, such as a hard drive, a USB (Universal Serial Bus) storage device, RAM (Random Access Memory), ROM (Read Only Memory), EPROM (Erasable Programmable Read Only Memory), or FLASH memory. A computer-readable medium can also be a data communication network, e.g., the internet, which allows the downloading of program code. In general, the computer-readable medium can be either non-volatile or volatile.

[0029] Another aspect of the invention relates to a control unit for a drive train, which is configured to carry out the method described herein. The control unit can have one or more processors and one or more memories in which the computer program described above is stored.

[0030] According to one embodiment, the control unit is a control system comprising a first control unit for providing the engine speed signal and a second control unit for determining the target speed signal. The control unit can be connected via a data communication bus, such as a CAN bus, which results in a delay of the engine speed signal and / or the target speed signal transmitted from the first control unit to the second control unit and / or from the second control unit to the control unit of the internal combustion engine. The speed signal can be delayed by a data communication bus used to transmit the engine speed signal and / or the target speed signal.

[0031] Another aspect of the invention relates to a drivetrain comprising the electric motor, the internal combustion engine, and a control unit as described herein. Further components of the drivetrain may include the clutch and / or a transmission that couples the drivetrain to the vehicle's wheels.

[0032] These and other aspects of the invention will become apparent and clear from the embodiments described below.

[0033] Embodiments of the present invention are described in more detail below with reference to the accompanying drawings. Fig. Figure 1 schematically shows a drive train according to an embodiment of the invention. Fig. Figure 2 shows a flowchart for a method for reducing vibrations according to an embodiment of the invention. Fig. Figure 3 shows a diagram illustrating the procedure according to Fig. 2 signals used and generated. Fig. Figure 4 shows a diagram illustrating how vibrations occur during the procedure according to Fig. 2 will be detected.

[0034] The reference symbols used in the drawings and their meanings are listed in summary form in the list of reference symbols. Identical parts in the figures are generally marked with the same reference symbols.

[0035] Fig. Figure 1 shows a powertrain 10, which can be, for example, a component of a hybrid vehicle. The powertrain comprises an internal combustion engine 12, a coupling 14, an electric motor 16, and a transmission 18. The electric motor 16 is directly connected to the transmission 18, i.e., independently of the open state of the coupling 14. The internal combustion engine 12 is coupled to the transmission via the coupling 14. In this way, the internal combustion engine 12 is coupled to the electric motor 16 via the coupling 14.

[0036] The electric motor 16, designed to propel the vehicle, is used to start the internal combustion engine 12. Initially, the coupling clutch 14 is open, and the internal combustion engine 12 is not running, i.e., it has zero rotational speed, while the electric motor 16 may be running, i.e., it has a positive rotational speed. To start the internal combustion engine 12, the clutch 14 is partially engaged, so that torque is transmitted to the internal combustion engine 12, which then begins to rotate, driven by the electric motor 16. Partially engaged means that the clutch 14 slips and / or the torque is only partially transmitted. When the internal combustion engine 12 reaches the same rotational speed as the electric motor 16, the clutch 14 is fully engaged.

[0037] In this process, the combustion engine 12 (e.g., its valves) must be controlled so that it operates at the same speed as the electric motor 16, which is also set to a higher speed during startup. Due to suboptimal control within the closed-loop system, particularly due to the processing times of a control system 20 of the drivetrain 10, vibrations may be generated.

[0038] This control system 20 comprises an internal combustion engine control unit 22, an engine control unit 24, and a transmission control unit 26, which communicate with each other via a data communication bus 28, such as a CAN bus. As indicated by the arrows, the engine control unit 24 transmits the actual engine speed 30 of the electric motor 16 to the transmission control unit 26 via bus 28. The transmission control unit 26 calculates a target speed 32 of the internal combustion engine 12, which is transmitted to the internal combustion engine control unit 22 via bus 28. All of this generates a latency, which, if the control system is unsuitable, can lead to vibrations in the drivetrain.

[0039] Fig. Figure 2 shows a method for reducing vibrations in the drive train 10, which is carried out automatically by the control system 20. The method can be carried out during synchronization of the internal combustion engine 12 with the electric motor 16, particularly when the clutch 14 is partially open. Such synchronization can be carried out during a start of the internal combustion engine 12 and / or during a closing of the clutch 14.

[0040] In step S10, a motor speed signal 30 from the electric motor 16 is received by the transmission control unit 26. The motor speed signal is provided by the motor control unit 24 of the electric motor 16, which determines the motor speed signal 30, for example, using a speed sensor of the electric motor 16. Optionally, the motor speed signal 30 is filtered in step S10 to remove ripples. The filtering can be performed using a low-pass filter. For example, averaging can be performed using a sliding window.

[0041] In step S12, the transmission control unit 26 determines an envelope signal 34 from the engine speed signal 30 and a target speed signal 32 from the envelope signal 34 by adding an offset signal 40 to the envelope signal 34. This is done with reference to Fig. 3 and Fig. 4 explained in more detail.

[0042] In step S14, the transmission control unit 26 sends the target speed signal 32 to the internal combustion engine control unit 22 of the internal combustion engine 12, which applies the target speed signal 32 to the internal combustion engine 12.

[0043] Fig. Figure 3 shows a diagram with the motor speed signal 30, the envelope signal 34 and the target speed signal 32. The signals are shown in relation to time, running to the right.

[0044] The envelope signal 34 is calculated from the engine speed signal 30 as follows: A local maximum 36 of the engine speed signal 30 is detected. When a local maximum 36 is detected, the envelope signal 34 is set to the value of the local maximum 36. The envelope signal 34 remains at the value of the local maximum 36 until the engine speed signal 30 rises above the local maximum 36 or until a time period 37 has elapsed since the local maximum 36. As in Fig. As can be seen in Figure 3, the target speed signal 32 is preferably kept above the engine speed signal 30, so that the envelope signal 34 is an upper limit of the raw signal and thus also the offset is in the positive direction. This has the advantage that synchronization is simpler when the internal combustion engine speed is above the engine speed, which is why the approach of selecting a local maximum 36 is particularly advantageous.

[0045] When the motor speed signal 30 rises above the value of the local maximum 36, the envelope signal 34 is adjusted to the motor speed signal 30. The envelope signal 34 is then adjusted to the values ​​of the motor speed signal 30 until the next local maximum 36 is detected. In this way, jumps in the envelope signal 34 can be avoided while the envelope signal still has a non-negative gradient.

[0046] Furthermore, the envelope signal 34 is set to the motor speed signal 30 when time period 37 has elapsed since the local maximum 36. A timer is always started when a local maximum is detected. When the timer has expired after time period 37, the envelope signal 34 is set to the motor speed signal 30. Time period 37 has a fixed length and / or was chosen with respect to an averaged period of the expected oscillations.

[0047] A local maximum can be detected by comparing values ​​of the motor speed signal 30 within a time window. If the highest value within the time window is not at the edge of the time window, then the highest value can be identified as the local maximum 36.

[0048] Furthermore, a gradient signal 38 can be generated from the motor speed signal 30 (see Fig. 4) The local maxima 36 are determined and detected from the zero crossings of the gradient signal 38. The values ​​of the gradient signal 38 at a given time are the gradient values ​​of the engine speed signal 30 at that time. The gradient signal 38 can be determined by measuring the differences between successive values ​​of the engine speed signal 30. When the gradient signal 38 transitions from positive to negative values, a local maximum 36 of the engine speed signal can be detected.

[0049] If vibrations are detected in the motor speed signal 30, an additional offset 35 and / or an offset signal 40 are generated (see Fig. 4) added to the envelope signal 34. The offset signal 40 is set to the offset value 35 when vibrations are detected, and the offset signal 40 is set to zero otherwise. The offset value 35 is a fixed value and / or was selected with respect to the expected amplitudes of the motor speed signal 30. For example, vibrations are detected when local maxima 36, ​​or more generally, local extrema, are spaced less than a vibration time window apart.

[0050] The offset 35 added to the envelope signal 34 ensures that the target speed signal 32 is higher than the engine speed signal 30 during the oscillations, so that even a delayed target speed signal 32 does not lead to a reduction in the speed of the internal combustion engine 12. The target speed signal 32 maintains a distance from the engine speed signal 30, resulting in a smoother synchronization of the internal combustion engine 12 with the electric motor 16.

[0051] Fig. Figure 4 shows a diagram illustrating how vibrations can be detected. Fig. Figure 4 shows a gradient signal 38, a second smoothed gradient signal 42, a band 44 around the second gradient signal 42, a timer 46, and the offset signal 40. Here too, the signals are shown in relation to time, which runs to the right.

[0052] The first gradient signal 38 and the second gradient signal 42 are determined from the motor speed signal 30, with the second gradient signal 42 being smoothed over a wider moving time window than the first gradient signal 38. For example, the second gradient signal 42 could be the first gradient signal 38 that has been smoothed. Smoothing could, for example, be performed by averaging over a moving time window.

[0053] The first gradient signal 38 is compared to a band 44 around the second gradient signal 42. Band 44 is defined by an upper band limit 44a and a lower band limit 44b. The upper band limit 44a is the second gradient signal 42 plus a threshold value. The lower band limit 44b is the second gradient signal 42 minus the threshold value. The threshold value can be determined with respect to an expected amplitude of the gradient signal 38.

[0054] Generally, a peak of the first gradient signal 38 is detected when the first gradient signal 38 leaves the band 44 and crosses the second gradient signal 42 within one oscillation time period 48. The oscillation time period 48 is determined by a timer 46, which is started when either the first gradient signal 38 leaves the band 44 or the first gradient signal 38 crosses the second gradient signal 42. The oscillation time period 48 may have been selected with respect to an expected oscillation length.

[0055] Vibrations are detected when one, two or more peaks of the first gradient signal 38 are detected.

[0056] In a first embodiment, vibrations are detected when, within the vibration time period 48, the first gradient signal 38 leaves the band 44 around the second gradient signal 42 and subsequently the first gradient signal 38 crosses the second gradient signal 42. In this way, a peak of a vibration can be detected and / or vibrations can be detected quickly.

[0057] In Fig. For example, the first gradient signal 38 leaves band 44 at point 50 and crosses the second gradient signal 42 at point 52 before the timer 46 has expired. Thus, a first peak is detected and the offset signal 40 is set to offset 35, as shown by the dashed line.

[0058] As a second example, it is additionally required that the first gradient signal 38 within the oscillation period 48 runs out of the band 44 around the second gradient signal 42 on the other side and then the first gradient signal 38 crosses the second gradient signal 42 again within the oscillation period 48.

[0059] In Fig. For example, the first gradient signal 38 leaves band 44 at point 54 before the timer 46 has expired and crosses the second gradient signal 42 at point 56 before the timer 46 has expired. Thus, a second peak is detected and the offset signal 40 is set to offset 35, as shown by the solid line.

[0060] Until peak values ​​are detected in this way and the timer 46 does not expire, the offset signal 40 remains at the offset value 35. Whenever the timer expires, as shown at point 58, the vibration detection is reset and the offset signal is reset to 0.

[0061] Even though the invention is illustrated and described in detail in the drawings and the preceding description, these illustrations and descriptions are to be considered illustrative or exemplary and not limiting; the invention is not limited to the disclosed embodiments. Other variations of the disclosed embodiments can be understood and implemented by a person skilled in the art who implements the claimed invention by studying the drawings, the disclosure, and the accompanying claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor, a single control unit, or other unit can perform the functions of several elements listed in the claims.The mere fact that certain measures are listed in different dependent claims does not mean that a combination of these measures cannot be advantageous. Any reference numerals in the claims are not to be understood as limiting the scope of the invention. Reference sign 10 Powertrain 12 Internal combustion engine 14 Clutch 16 Electric motor 18 gearboxes 20 Control unit / control system 22 Internal combustion engine control unit 24 Engine control unit 26 Transmission control unit 28 Data communication bus 30 Engine speed signal 32 Target speed signal 34 Envelope signal 35 Offset 36 local maximum 37 Time period 38 (first) gradient signal 40 Offset signal 42 second gradient signal Volume 44 44a upper band limit 44b lower band limit 46 timers 48 oscillation period

Claims

[1] Method for reducing vibrations in a powertrain (10) wherein the powertrain (10) comprises an electric motor (16) and an internal combustion engine (12) coupled together, wherein the method comprises: Receiving a motor speed signal (30) from the electric motor (16); Determining a target speed signal (32) for the internal combustion engine (12) by modifying the engine speed signal (30) into an envelope signal (34); Applying the target speed signal (32) to the internal combustion engine (12); wherein the envelope signal (34) is calculated by detecting a local maximum (36) of the engine speed signal (30), setting the envelope signal (34) to the value of the local maximum (36) after the local maximum (36) and resetting the envelope signal (34) to the engine speed signal (30) when a time period (37) starting with the local maximum (36) has elapsed. [2] Method according to claim 1, wherein the envelope signal (34) is adjusted to the motor speed signal (30) when the motor speed signal (30) rises above the local maximum (36). [3] Method according to claim 1 or 2, wherein a gradient signal (38) is determined from the motor speed signal (30) and the local maxima (36) are detected either from zero crossings of the gradient signal (38) or by comparing old gradient values ​​with the current cycle value of the gradient, in particular where the gradient changes its direction from an increasing tendency to a decreasing tendency. [4] Method according to any of the preceding claims, wherein the target speed signal (32) is determined by adding an offset signal (40) to the envelope signal (34); wherein the offset signal (40) is set to an offset value when vibrations are detected in the motor speed signal (30), and otherwise the offset signal (40) is set to zero. [5] Method according to claim 4, wherein a first gradient signal (38) and a second gradient signal (42) are determined from the motor speed signal (30), wherein the second gradient signal (42) has been smoothed with respect to a wider sliding time window than the first gradient signal (38); where the vibrations are detected when: the first gradient signal (38) emerges from a band (44) around the second gradient signal (42), and then the first gradient signal (38) crosses the second gradient signal (42) within one oscillation period (48). [6] Method according to claim 5, wherein vibrations are detected when: the first gradient signal (38) runs out of the band (44) around the second gradient signal (42), and then the first gradient signal (38) crosses the second gradient signal (42) within the oscillation time period (48), and then the first gradient signal (38) within the oscillation time period (48) runs out of the band (44) around the second gradient signal (42) on the other side, and then the first gradient signal (38) crosses the second gradient signal (42) again within the oscillation time period (48). [7] Method according to one of the preceding claims, wherein the motor speed signal (30) is filtered to remove ripples before calculating the envelope signal (34). [8] Method according to any one of the preceding claims, wherein the procedure is carried out during a synchronization of the internal combustion engine (12) with the electric motor (16); wherein the internal combustion engine (12) and the electric motor (16) are coupled by a clutch (14); wherein the clutch (14) is partially open during the synchronization of the internal combustion engine (12) with the electric motor (16). [9] Method according to claim 8, wherein the method is carried out during the start of the internal combustion engine (12) during the closing of the clutch (14). [10] Computer program with instructions which, when the program is executed by a processor, cause the processor to execute the method according to any of the preceding claims. [11] Computer-readable medium in which a computer program according to claim 10 is stored. [12] Control device (20) for a drive train (10) suitable for carrying out the method according to any one of claims 1 to 9. [13] Control device (20) according to claim 12, wherein the control device (20) comprises a first control device (24) for providing the engine speed signal (30) and a second control device (26) for determining the target speed signal (32), which are connected via a data communication bus (28), resulting in a delay of the engine speed signal (30) and / or the target speed signal (32). [14] Powertrain (10), comprising: an electric motor (16); an internal combustion engine (12); a control device (20) according to claim 12 or 13.

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